BUG#37631 - Incorrect key file for table after upgrading from 5.0 to 5.1

This patch adds corrections to the original patch
submitted 2009-04-08 (http://lists.mysql.com/commits/71607):

- fixed that the original patch didn't work because of an
  incorrect condition;
- added a test case.

mysql-test/r/upgrade.result

@@ -57,6 +57,18 @@ s1
 1
 drop table `txu@0023p@0023p1`;
 drop table `txu#p#p1`;
+#
+# Bug#37631 Incorrect key file for table after upgrading from 5.0 to 5.1
+#
+# copy table created using mysql4.0 into the data dir
+# check the table created using mysql 4.0
+CHECK TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	check	error	Table upgrade required. Please do "REPAIR TABLE `t1`" or dump/reload to fix it!
+# query the table created using mysql 4.0
+SELECT * FROM t1;
+c1	c2	c3
+DROP TABLE t1;
 truncate t1;
 drop table t1;
 drop database if exists `tabc`;

mysql-test/t/upgrade.test

@@ -48,6 +48,20 @@ select * from `txu#p#p1`;
 drop table `txu@0023p@0023p1`;
 drop table `txu#p#p1`;
 
+--echo #
+--echo # Bug#37631 Incorrect key file for table after upgrading from 5.0 to 5.1
+--echo #
+--echo # copy table created using mysql4.0 into the data dir
+let $MYSQLD_DATADIR= `SELECT @@datadir`;
+copy_file std_data/bug37631.frm $MYSQLD_DATADIR/test/t1.frm;
+copy_file std_data/bug37631.MYD $MYSQLD_DATADIR/test/t1.MYD;
+copy_file std_data/bug37631.MYI $MYSQLD_DATADIR/test/t1.MYI;
+--echo # check the table created using mysql 4.0
+CHECK TABLE t1;
+--echo # query the table created using mysql 4.0
+SELECT * FROM t1;
+DROP TABLE t1;
+
 #
 # Check if old tables work
 #

storage/myisam/ha_myisam.cc

@@ -392,7 +392,7 @@ int check_definition(MI_KEYDEF *t1_keyinfo, MI_COLUMNDEF *t1_recinfo,
                             test(t2_keyinfo[i].flag & HA_SPATIAL)));
        DBUG_RETURN(1);
     }
-    if ((mysql_40_compat &&
+    if ((!mysql_40_compat &&
         t1_keyinfo[i].key_alg != t2_keyinfo[i].key_alg) ||
         t1_keyinfo[i].keysegs != t2_keyinfo[i].keysegs)
     {
@@ -424,7 +424,7 @@ int check_definition(MI_KEYDEF *t1_keyinfo, MI_COLUMNDEF *t1_recinfo,
           t1_keysegs_j__type= HA_KEYTYPE_VARBINARY1; /* purecov: inspected */
       }
 
-      if ((mysql_40_compat &&
+      if ((!mysql_40_compat &&
           t1_keysegs[j].language != t2_keysegs[j].language) ||
           t1_keysegs_j__type != t2_keysegs[j].type ||
           t1_keysegs[j].null_bit != t2_keysegs[j].null_bit ||